Railway track circuit apparatus



May 22, 1951 Filed Feb. 26, 1947 J. E. HlLLlG ET AL RAILWAY TRACKCIRCUIT APPARATUS 2 Sheets-Sheet 1 gNVENTORS Jahn .Hziiz'g and BY E y 2,1951 J. E. HILLIG ET AL 2,554,460

RAILWAY TRACK CIRCUIT APPARATUS Filed Feb. 26, 1947 2 Sheets-Sheet 2INVENTORS. Jalzn EHL'Zlzy and BY E wil a qlz Tizezk Afplzeg.

Patented May 22, I951 RAILWAY TRACK CIRCUIT APPARATUS John E. Hillig,Philadelphia, and Earl W. Reich, J enkintown, Pa.

Application February 26, 1947, Serial No. 730,976

13 Claims.

Our invention relates to railway track circuit apparatus, and moreparticularly to such apparatus using electron tubes.

In railway track circuits, shunting sensitivity, broken rail protection,broken down insulated rail joint detection, and reliability areimportant operating characteristics. Also, a closed circuit principle isessential to assure that a failure of a component of the circuit willcause a restrictive signal indication.

It is a main object of our invention to provide novel and improvedrailway track circuit apparatus which is characterised by high shuntingsensitivity and which maintains the high shunting sensitivity over awide variation of ballast resistance and under adverse shuntingconditions due to a film of relatively high resistance on the railsurface.

A more specific object of our invention is the provision of railwaytrack circuit apparatus using electron tubes in a novel and improvedarrangement to provide high shunting sensitivity, broken railprotectionto a high degree of safety, broken down insulated jointprotection and to cause a restrictive signal indication when one or morecomponents fail.

Again, a feature of our invention is the provision of track circuitapparatus of the form here contemplated for crossovers giving protectionfor the complete crossover and maintaining the inwhich controlelectromagnetic relays governing the conventional signal circuits. Thesetubes are preferably ionization tubes and tube conduction is controlledby phasing the alternating voltages applied to the anode and controlelectrodes as well as by the magnitude of such voltages.

For one of the tubes, a negative bias potential of a specific value isapplied to a shield grid so that there is a critical positive value ofthe control grid potential to cause the tube to conduct during thepositive half cycle of the alternating r current wave applied to theanode. The critical voltage necessary to determine tube conductionisderived from the rail circuit. Thus this tube isfiredalternate halfcycles of the alternating track circuit current when the track circuitis unoccupied and the voltage across the track rails is not less than agiven critical value. When the track rails are shunted even with arelatively high resistance shunt, the voltage applied to the controlgrid falls below the critical value and the tube fails to conduct. Thetube and its circuits are characterized by steep controlcharacteristics: and a high circuit sensitivity is obtained.

A limiting impedance preferably comprising a resistor and an input orprimary winding of a step-up transformer in parallel is connected acrossthe rails of the track circuit. The Value of this impedance limits thevalue of the maxi.- mum ballast resistance of the track circuit, thatis, the resistance from one rail to the other. This limiting of theballast resistance tends to maintain the shunting sensitivity obtainedby the aforementioned tube substantially uniform over a wide variationof the leakage resistance of. the ballast as caused by variations ofweather conditions.

A break in a rail, which inserts the additional resistance of a leakagepath through the ballast and ground around the break in series in therail circuit, will reduce the voltage applied to the input of the tubeand it will fail to conduct. This arrangement provides broken railprotection because steep operating characteristics of the tube can beprovided so that a relatively small. increase in the rail resistanceresults in a non-conductive condition of the tube. A ballast resistancelower than the maximum value will lower the. voltage applied to the tubeand the broken rail protection is not decreased by a low ballastresistance.

The voltages applied to an anode and shield grid of a second electrontube are obtained from secondary windings of the step-up transformer. Acontrol grid of this second tube is provided with a fixed potential andthe control grid potential'is selected to permit the tube to conductwhen the anode and shield grid voltages are of values resulting from thevoltage applied to the input winding of the step-up transformer undernormal ballast resistance of the track circuit.

This second tube serves to check the integrity of the limiting impedancewhich maintains a uniform high shunting sensitivity for the firstelectron tube.

The track transformers of adjacent trackv circuits are connected tosupply currents of opposite instantaneous polarities so that a brokendown insulated rail joint which permits current tobe fed to the trackrelay means for one track circuit from the track transformer of theadjacent track: circuit through the insulated rail jointswillz: apply 3to the tubesof the track relay means potentials out of phase and thetubes will fail to conduct with the result a restrictive signalindication is displayed as a detection of the defective insulated railjoint.

The tube circuits are arranged in such a manner that the bias voltagesare checked and a loss of a bias voltage due to a broken connection orpoor contact results in the tube being non-conductive corresponding to arestrictive traffic condition of the associated track circuit.

We shall describe two forms of apparatus embodying our invention, andshall then point out.

the novel features thereof in claims.

In the accompanying drawings,

Fig. 1 is a diagrammatic view showing one form of track circuitapparatus embodying our invention, and Fig. 2 is a diagrammatic viewshowing track circuit apparatus embodying our invention when applied toa crossover.

In each of the two views like reference characters are used to designatesimilar parts.

Referring to Fig. l, the reference characters Ia..and Ib designate thetrack rails of a railway over which traffic normally moves in thedirection indicated by the arrow, and which rails are divided by theusual insulated rail joints into consecutive track sections of asignaling system, and of which sections only the one section K-L andtheladjoining end of an adjacent section are shown, since these aresufiicient for a full understanding of our invention. Each section isprovided with track circuit apparatus embodying our invention and whichapparatus comprises a source of alternating current connected acrosstherails at one end of the section and an electron tube track relaymeans connected across the rails at the other end of the section. Thesource of supply for the track circuits is a generator G connected to apair of line wires LI and L2 extending along the railway. The generatorG supplies alternating current preferably of a frequency of the order of.00 cycles per second, but other frequencies can be used.

Power is supplied to the track circuits through track transformers ofthe usual construction. For example, a' track transformer TI for thetrack circuit of section K-L has a primary winding I6 connected acrossthe line wires LI and L2 and a secondary winding I I connected acrossthe track rails at the exit end L of the section, a current limitingresistor HI I being interposed in the connection to the rail Ib.Similarly, a track transformer T4 for the track circuit of the sectionnext to the left of section KL as viewed in Fig. 1, has a primarywinding I2 connected across the line Wires and a secondary winding I3connected across the rails through a resistor RI 3. For reasons to beexplained hereinafter, the connections of the track transformers TI andT5 are arranged so that currents of reverse instantaneous polarity aresupplied to the adjacent track circuits, the plus and minus signs placedat the track transformers indicating the polarity of the currents at agiven instant.

The track relay means for the track circuits are alike and only that forthe circuit of section KL is shown. This track relay means includes asupply transformer T2, a step-up transformer T3, a limiting resistor R7,two electron tubes DI and D2 and two relays A! and A2, together withassociated tube circuits.

The supply transformer T2 is provided with a primary winding I4receiving power from the line wires LI and L2 and with a group ofindependent secondary windings A, B, C, D, and E to be referred to fromtime to time. To aid in the understanding of the apparatus, the polarityof the voltages of the several secondary windings of transformer T2 at agiven instant is indicated by plus and minus signs placed at thesecondari windings.

The step-up transformer T3 has an input or primary winding 15 connectedin parallel with resistor R1 across the track rails to provide alimiting impedance, and transformer T3 receives power from the trackcircuit. Transformer T3 is provided with two secondary windings AA andBB, to be referred to later.

The electron tubes DI and D2 are preferably alike and as here shown theyare four-element Thyratrons of the indirectly heated cathode type, butother types of tubes can be used. Tube DI, for example, is provided withan anode I5, a shield grid Il', a control grid I8 and a cathode I9,together with a heater or filament 2B. Similary, tube D2 has an anode2|, a shield grid 22, a control grid 23 and a cathode 24, together witha filament 25. Each of the tubes DI and D2 is so constructed that itsshield grid (ll of tube DI and 22 of tube D2) is provided with twoterminals. With this construction, the connection to the shield grid ismade to include the two terminals and the grid element in series. Thisseries arrangement assures that any break in the connection or the gridwill open the associ ated circuit and detect the loss of the shield gridcontrol.

The relays AI and A2 are neutral magnetic r relays of standardconstruction and each is equipped with contacts to govern conventionalsignal circuits in the usual manner.

The secondary winding B of power transformer T2 is connected to theinput terminals of a full wave rectifier 26 in series with apotentiometer resistor R5, and the output terminals of the rectifier areconnected to the heater 20 of tube DI. That is, the voltage supplied bysecondary winding B serves to heat the tube DI and to provide analternating voltage drop across resistor R6, and which voltage drop isused to bias the shield grid ll of the tube as will shortly appear.

An anode-shield grid circuit for tube DI can be traced from theleft-hand terminal ofsecondary winding A of transformer T2, throughresistor RI, winding of relay AI, anode I6 and tube space to cathode IQof the tube DI, resistor R6 to an intermediate terminal 21, one terminalof shield grid I! and the grid element to the other terminal of the gridand thence to the other terminal of secondary winding A. The voltage ofsecondary winding A modified by the voltage drop of a portion ofresistor R6 is impressed across the anode and cathode of tube DI tendingto firethe tube. Also, the voltage drop across a portion of resistor R6as determined by the setting of the intermediate terminal 21 serves tobias the shield grid I'I. With instantaneous polarity of the voltages ofsecondary windings A and B as indicated by the plus and minus signs,then during the half cycle of the voltage that the anode I5 is positivein potential with respect to the cathode I9, the shield grid I! isnegative in potential with respect to the cathode by a voltage, thespecific value of which is determined by the setting of terminal 21 ofresistor R6. The parts are so proportioned that the tube DI fails toconduct at the voltage supplied to the anode from the secondary windingA without suitable voltage on'the control grid due to the negative biasof the shield grid. Furthermore, the bias potential applied to theshield grid is made such that a definite control grid potential isrequired to create a conductive condition of the tube.

The tube BI is provided with a control grid circuit that can be tracedfrom rail lb through a resistor R9 to control grid l8, and from. cathodel9 through the secondary winding C of transformer T2 to rail la. Thus avoltage derived from track transformer Tl through the rail circuit and avoltage from secondary winding C of the power transformer T2 are appliedto the control grid of tube Di in series. The connections of secondarywinding ll of transformer Tl and secondary winding C of transformer T2are such that the polarities of their voltages at a given instant areindicated by the plus and minus signs and the two voltages are additiveas applied to the control grid 58. Furthermore, the winding ll and thewinding C are'connected so that the voltage applied to the control gridit causes the grid it to be positive in potential with respect to thecathode l5 during the half cycle of the alternating current the anode I5is positive with respect to the cathode. The parts are so proportionedthat the voltage from winding C alone is insufiicient to cause the tubeto conduct, but that the voltage resulting from the addition of thevoltage of winding C and the voltage derived from the track circuit issufficient to fire the tube and current flows to energize the relay Alinterposed in the anode circuit. By making the voltages of secondarywindings C and II additive, it is not necessary to impress a highvoltage across the rails, yet it allows for a critical voltage to beapplied to the control grid of tube DI from the rail circuit before thetube is fired. During the negative half cycle of the alternatingcurrent, the negative voltage applied to the anode I 6 stops theconduction of current so that the tube DI becomes deionized and thecontrol grid l8 regains control. That is, the tube Dl is made conductiveduring alternate half cycles of the alternating current and relay Al isenergized with periodic impulses of current. series are connected acrossthe winding of relay Al and relay Ai thereby is made slow releasing incharacter and is retained picked up during the half cycle of thealternating current that the tube- Relay Al governs at its:- frcntcontact Eli a conventional signal circuit in.

D5 is non-conductive.

the usual manner.

It follows that tube Dl is provided with aspecific bias voltage for itsshield grid to assure 3 that the tube is not conductive at the voltage"applied to the anode without suitable voltage on the control grid andthe series arrangement of the anode and shield grid checks the presenceofthis shield grid bias. The control voltage applied to rails will lowerthe voltage applied to the control grid sufficiently for the tube tofail to conduct and relay Al will be deenergized to control the signal'circuit. Also, proper shunting of the track circuit will be eilectedwhen the track is infrequently used and a film of relatively highresistance is: present on the rail surfaces. Furthermore, av break inthe electrical continuity of the rails la and lb will lower the voltageapplied to tube DI and the tube will fail to conduct and thereby detectthe broken rail condition.

A capacitor 28 and a resistor 29 in curs-sued 7 of the track circuit,that is, the rail to rail impedance, and consequently a more nearlyuniform shunting sensitivity of the track circuit is main= tained for arelatively wide variation of the leakage resistance as caused by changein weather conditions. Although we prefer to use resistor R7 and aninput winding of transformer T3 in parallel as the limiting impedance,it is clear that the resistor B? may be omitted and the input winding ofthe transformer made to have the desired impedance.

The heater of tube D2 is energized from secondary winding D oftransformer T2 and control grid 23 of tube D2 is provided with a controlpotential from secondary winding E of transformer T2 a resistor Ell}being preferably included in the connection of grid '23. An anodeshieldgrid circuit for tube D2 can be tracedfrom the top terminal of secondarywinding AA'of transformer T3, through resistor R3, winding of relay A2,anode El and tube space to cathode 24 of tube D2, secondary winding B3of transformer T3, one terminal to the other of shield grid 22, and tothe other terminal of secondar winding AA. Since the input winding iiiof transformer T3 isconnected across the rails, the voltages induced insecondary windings AA and BB of transformer T3 are determined by thecurrent flowing in the rails from the track transformer Tl. Theconnections are such that the instantaneous p0 larity of the voltages ofsecondary winding ll of track transformer T l and secondary windings AAand BB of transformer T3 are as indicated "by the plus and minus signsplaced on the windings. This means that during the half cycle of thealternating current the tube Dl is made conductive as explainedhereinbefore, the voltage applied to tube D2 causes the anode El to benega'- tive in potential with respect to the cathode 24 and the tube D2is non-conductive. During the next half cycle of the alternating currentthe anode Zl is made positive tending to me the tube D2. It is notedthat during the half cycle that anode Zl is positive, the shield grid 22is driven negative in potential with respect to the cathode by thevoltage of secondary winding BB. The parts are so proportioned that thenegative bias of the shield grid is sufficient to keep the tube D2non-conductive without suitable potential applied to the control grid.However, the secondary winding E. is poledso that the control grid 23 ispositive in potential with respect to the cathode during the half cycleanode 2l is -posi-' tive and such positive bias voltage for the controlgrid 23 serves to counteract the negative bias of the shield grid 22 andthe tube D2 is fired. With tube D2 made conductive, the relay A2 isenergized by an impulse of anode current. A capacitor 39 and resistoriii in series are connected across the winding of relay A2, andrelay A2is retained energized and picked up during the half cycle of thealternating current that ztube D2 is non-conductive. Relay A2 controlsthe conventional signal circuit at its front contact 5 l.

The control grid voltage for tube D2-as derived .from secondary windingE is selected to permit conduction of the tube when the voltage applied'to the input winding E5 of transformer T3 is that created under normalor maximum ballast resistance of the track circuit with the resistor R?intact and the track circuit unoccupied.

Preferably, the parts are proportioned so that the tube D2 is operatedon a, range of its characteristic curves where an increase in thenegative shield grid potential is more effective than a correspondingincrease in the positive anode potential and where a decrease in thenegative shield grid potential is less effective than a correspondingdecrease in the positive anode potential. This means that a givenincrease in the voltage applied to the input winding I of transformer T3to cause corresponding increases in the voltages of secondary windingsAA and BB will make the tube D2 non-conductive, and also a givendecrease in the voltage applied to input winding I5 to causecorresponding decreases in the voltages of windings AA and BB will makethe tube nonconductive. 7

Thus the tube D2 serves to check the integrity of the limiting impedancemade up of resistor R1 and input winding I5, and which limitingimpedance assures a substantially uniform shunting sensitivity of thetrack circuit as provided by tube DI. If winding I5 is open circuited,tube D2 becomes inactive and relay A2 is deenergized. If resistor R1 isopen circuited, the voltage applied to input winding I5 is materiallyincreased and the voltages induced in secondary windings AA and BB arecorrespondingly increased and tube D2 becomes non-conductive todeenergize relay A2.

Furthermore, a decrease in the voltage applied to input winding I5 oftransformer T3 due to a train shunt or a, broken rail will lower thevoltages induced in secondary windings AA and BB and tube D2 becomesnon-conductive to detect the train shunt or broken rail, this detectioneifected by tube D2 being supplemental to the detection obtained by tubeDI With the track transformers Ti and T4 connected to supply currents ofreverse relative polarity for the track circuits, it is clear that if aninsulated rail joint at location K fails and current from tracktransformer T4 is fed to the tubes DI and D2, such current would causethe tubes to be non-conductive and the relays AI and A2 to be released.This is so because the voltage applied to control grid I8 of tube DIfrom transformer T l through a defective insulated rail joint will beout of phase with the voltage applied to anode I8, and the voltageapplied to anode 2I of tube D2 from transiormer T4 through the insulatedrail joint will be out of phase with the voltage applied to control grid23. Consequently the tubes DI and D2 provide broken down insulated railjoint protection.

Referring to Fig. 2, two main tracks IT and 2T are joined by a crossover3T, the two switches ISW and ZSW of the crossover being indicated as ofthe hand throw type although they can be power operated. The track IT isformed with a track circuit KILI including track switch ISW and having atrack battery 35 and a track relay 36. Similarly, the main track 2T isformed with a track circuit K2-L2 including track switch ZSW and havinga, track battery 31 and a track relay 3B. The track circuit KILIcontrols signals governing traffic on the main track IT and the trackcircuit K2--L2 controls signals governing trafilc on track 2T in any ofthe well-known arrangements. These two track circuits should beinsulated one from the other so that trafiic moving on track IT throughthe track circuit KI-LI will not interfere with the signals controllingtrafiic on track 2T and vice versa.

The crossover ST is formed by insulated rail joints with two sections UVand VW. The

insulated rail joints 9 at the junction of the two sections of thecross-over are by-passed by capacitors 39 and 40.

The two sections of crossover 3T are included in series in a trackcircuit, the apparatus of which is substantially the same as thatdescribed in connection with Fig. l. A track transformer T5 has asecondary winding 4| connected across the rails at one end of section VWand an electron tube track relay means is connected across the rails atone end of the section UV. The track relay means includes electron tubesDI and D2 and relays AI and A2, together with associated circuits thesame as in Fig. 1, and the description need not be repeated. Thecrossover track circuit apparatus of Fig. 2 receives power from thetrack transformer T5 due to the insulated joint 9 being by-passed by thecapacitors 39 and 40.

In Fig. 2 the source of alternating current is a generator GI having itsterminals connected to conductors 42 and 43 for supplying alternatingcurrent to the track transformer T5 and to a power transformer T2. Thegenerator GI provides alternating current of a suitable frequency suchas, for example, of the order of 60 or cycles per second. An alternatingcurrent of a relatively high frequency of the order of 1000 cycles persecond or higher can be used, such high frequency serving to reduce thesize of the capacitors 39 and 40 which are proportioned to pass thealternating current from generator GE and to block the current used forthe track circuits for the main tracks IT and ET. Under thesecircumstances, the track circuit for sections U-V and VW has operatingcharacteristics the same as those described for the apparatus of Fig. 1.

It is clear that the arrangement of Fig. 2 provides protection for thecomplete crossover I3 and the track circuits for the main tracks IT and2T are in effect electrically insulated one from the other.

Track circuit apparatus here disclosed has the advantage of providing ahigh shunting sensitivity for a wide differential between low and highballast resistance, thatis, the resistance of the ballast, ties, etc.,from one rail to the other. The limiting impedance comprising resistorR! and winding l5 stabilizes the rail-to-rail impedance so that ballastresistance variations do not greatly vary the rail-to-rail impedance.The tube DI is characterized to require but a small control grid voltagevariation to change the tube DI from a conductive to a non-conductivecondition. Thus, a relatively high train shunt resistance will decreasethe rail-to-rail voltage sufficiently to switch the tube DI to anon-conductive condition. This assures that a train or even a singlecar, occupying a track circuit infrequently used and with a highresistance film present on the surface of the rails, will be detected.In other words, the tube DI functions as a track relay having a releasevoltage only slightly less than the pick-up voltage. The track circuitapparatus here disclosed also has the advantage of providing broken railprotection of a high degree of safety between maximum and minimum valuesof ballast resistance, because a relatively small resistance interposedin series in the rail circuit will lower the rail current sufficientlyfor the voltages applied to tube DI to be varied enough to change thattube to a non-conductive condition. Again, the track circuit apparatushere disclosed assures broken down insulated rail joint detection andchecks the components of the circuits. Furthermore the track circuits ofthe associated main tracks are electrically insulated one from theother.

We have disclosed track circuit apparatus which includes two electrontubes, one tube DI arranged to provide shunting sensitivity and 1 brokenrail protection and one tube D2 arranged to check the component parts ofthe circuit, and

' we prefer such a two-tube arrangement because each tube can beadjusted to perform its particular function with a high degree ofefliciency.

However, it is apparent that tube D2 will respond to a train shunt andbroken rail and consequently the track circuit apparatus here disclosedcan be arranged to use only tube DI or only tube D2, and our inventioncontemplates such modifications.

Although we have herein shown and described but two forms of railwaytrack circuit apparatus embodying our invention, it is understood thatvarious changes and modifications may be made therein within the scopeof the appended claims without departing from the spirit and scope ofour invention.

Having thus described our invention, what we claim is;

1. In a railway track circuit for a stretch of track, a source ofalternating current having connections to the rails of said stretch topower the track. circuit, a pair of controlled ionization electrontubes, means to excite an anode-cathode circuit of a first one of saidtubes but normally ineffective to fire the tube, a control grid-cathodecircuit for said first tube receiving, voltage from said track circuitto fire the tube on alternate half cycles of the alternating currentwhen the section is unoccupied, a transformer having an input windingconnected across the rails of said section to limit the rail-to-railimpedance of said track circuit and to be energized bythe track circuitcurrent, said transformer having a secondary winding connected to ananode-cathode circuit of a second one of said tubes to fire the, secondtube alternate half cycles of the alternating track circuit current tocheck the limiting impedance, and signaling means controlled by thecurrent impulses thus caused to flow in the anode-cathode circuits ofsaid tubes.

2. In a railway track circuit for a stretch of track, a source ofalternating current having connections to the rails of said stretch topower the track circuit; a first and a .econd controlled ionizationelectron tube each having an anode,

a cathode and at least one control grid; means to energize ananode-cathode circuit of said first tube from said current source, acontrol gridcathode circuit for said first tube connected to the railsof said stretch to fire the tube in response to alternate half cycles ofthe track circuit current when the stretch is unoccupied, a transformerhaving an input winding connected across the rails of said stretch to beenergized by the track circuit current, an impedance unit connected inmultiple with said input winding to pr determine in conjunction with theinput winding a maximum limit for the rail-to-rail impedance of saidtrack circuit, a control grid-cathode circuit for said second tubeexcited by said cur rent source, an anode-cathode circuit for saidsecond tube including a secondary winding of said transformer to firethe tube in response to alternate half cycles of the track circuitcurrent to check the impedance predetermined by said ill i0 r unit andinput winding, and signaling means controlled by said anode-cathodecircuits.

3. In a railway track circuit for a stretch of track, a source ofalternating current having connections to the rails of said stretch topower the track circuit; a first and a second controlled ionizationelectron tube each having an anode, a cathode and at least one controlgrid; means to energize an anode-cathode circuit of said first tube fromsaid current source but ineffective to 'fire the tube, a controlgrid-cathode circuit for said first tube connected tov the rails of saidstretch to fire the tube in response to alternate half cycles of thetrack circuit current when the stretch is unoccupied, a resistor, atransformer,

said resistor and an input winding of said transformer in parallelconnected across the rails of said stretch to limit the rail-to-railimpedance to maintain substantially uniform the shunting sensitivity ofthe said track circuit as provided by said first tube, a controlgrid-cathode circuit for said second tube excited from said currentsource, an anode-cathode circuit for said second tube including asecondary winding of said transformer to render the second tubeconductive in response to alternate half cycles of the voltage inducedin said secondary winding due to track circuit current flowing in saidinput winding to check the continuity of said resistor, and signalingmeans controlled by the anode-cathode .circuits of said tubes.

4. In a railway track circuit including the track rails of a stretch oftrack, a source of alternating current having connection to the rails ofsaid stretch to supply alternating current to said track circuit; afirst and a second gas tube each having an anode, a cathode and acontrol electrode; means to excite an anode-cathode circuit of saidfirst tube but ineffective to fire the tube, means to connect saidcontrol electrode and cathode of said first tube across the rails ofsaid stretch to render the tube conductive alternate half cycles of thetrack circuit current when the stretch is unoccupied, said first tubebeing non-conductive in response to a relatively high resistance shuntof the rails due to the operating characteristic of the tube, atransformer having an input winding connected across the rails of saidstretch to be energized by said track circuit current, an impedance unitconnected to said winding, said unit and input winding proportioned fora given impedance to preselect the maximum rail-to-rail impedance of thetrack circuit, control means to energize the control electrode of saidsecond tube, an anode-cathode circuit for said second tube including asecondary winding of said transformer to fire that tube alternate halfcycles of the track circuit current, said control means and saidsecondary winding proportioned to render the second tube nonconductivein response to a given variation in the impedance above or below saidgiven impedance of said unit and input winding, and signaling meanscontrolled by said anode;- cathode circuits of said tubes.

5. In a track circuit including the track rails of a stretch of track, asource of alternating current having connections to the rails at one endof said stretch to supply current to said track circuit; a controlledionization electron tube hav.-' ing an anode, a cathode and a controlelectrode; a transformer having an input winding corrnected across therails at the other end of the stretch to be energized by said trackcircuit cur-; rent, a control electrode-cathode circuit con-5 nectedacross the control electrode and cathode 11 of said tube and excitedbyacurrent source to establish a sensitivity for the tube preselected by'the voltage of the exciting current source, an anode-cathode circuitconnected across the anode and cathode of said tube and including asecondary winding of said transformer to fire the tube in response toalternate half cycles of the voltage induced in said secondary windingdue to the track circuit current flowing in said input winding, and acontrol relay energized by the current impulses created in saidanode-cathode circuit.

- 6. In a track circuit including the track rails of a stretch of track,a source of alternating current connected across the rails of saidstretch to supply current to said track circuit; a gas tube having ananode, a cathode and a first and a second control electrode; atransformer having an input winding connected across the rails of saidstretch to receive energy from the track circuit, a circuit includingsaid first control electrode and cathode to excite the first controlelectrode from said alternating current source; another circuitincluding in series a first and a second secondary winding of saidtransformer, said anode, said cathode and said second control electrode;said first and second secondary windings poled for said anode to bepositive in potential and said second control electrode negative inpotential with respect to said cathode the half cycle of the alternatingcurrent that said ,firt control electrode is positive in potential withrespect to the cathode whereby said tube is fired alternate half cyclesof track circuit current of a given value, and a relay having a windinginterposed in said another circuit to be energized by the impulses ofcurrent thus caused to flow in said another circuit.

7. In a track circuit including the track rails of a stretch of track, asource of alternating current connected across the rails of said stretchto supply current to said track circuit; a gas tube having an anode, acathode and a first and a second control electrode; a resistor, atransformer, said resistor and an input winding of said transformer inparallel connected across the rails of the stretch to provide a limitingrailto-rail impedance for the track circuit; a first circuit to connectsaid current source to said first control electrode and cathode toexcite the first control electrode; a second circuit including in seriesa first secondary winding of said transformer, said anode, said cathode,a second secondary winding of said transformer and said second controlelectrode to excite the anode and .second control electrode by trackcircuit current ,flowing in said input winding; said first and secondsecondary windings poled for said anode to be positive in potential andsaid second control electrode negative in potential with respect to saidcathode the half cycle of the alternating current that said firstcontrol electrode is driven positive in potential with respect to thecathode to fire the 'tube alternate half cycles of current received fromthe track circuit of a given range of values, and said tube and saidfirst and second circuits selected to operate the tube for the tube tobe non-conductive when the current flowing in said input winding isdecreased or increased beyond said given range of values.

8. In a track circuit including the track rails of a stretch of track, asource of alternating current connected across the rails of said stretchto supply alternating current to said track circuit; an indirectlyheated gas tube having an anode, a,

12 cathode and a first and a second control electrode; a powertransformer having its primary winding receiving power from said currentsource, a first secondary winding of said transformer connected inseries with a resistor to the input terminals of a full wave rectifierthe output termina1s of which rectifier are connected to a heaterelement of said tube; an anode circuit including a second secondarywinding of said transformer, anode to cathode space of said tube, atleast a portion of said resistor and said second control electrode; saidfirst and second secondary windings poled for said anode to be positivein potential and said second control electrode negative in potentialwith respect to said cathode during a given half cycle of saidalternating current to normally render the tube non-conductive, acontrol circuit including a third secondary winding of said transformerto connect said first control electrode and cathode across the rails ofsaid stretch to drive said first control electrode positive in potentialwith respect to the cathode said given half cycle of the alternatingcurrent to fire the tube when said stretch is unoccupied, and a controlrelay having a winding interposed in said anode circuit to energize therelay in response to the impulses of current passed by the tube.

9. In a track circuit including the track rails of a stretch of track, asource of alternating current connected across the rails of saidstretclt to supply current to said track circuit; an indi rectly heatedgas tube having an anode, a cathode and a first and a second controlelectrode; a power transformer having a primary winding receiving powerfrom said current source, a first circuit including a resistor toconnect a first sec-- ondary winding to a heater element of said tube;'an anode circuit including in series a second secondary winding of saidtransformer, anode-tocathode space of said tube, at least a portion ofsaid resistor and said second control electrode; said first and secondsecondary windings poled for said anode to be positive in potential andsaid second control electrode negative in potential with respect to thecathode during a given half cycle of the alternating current to normallymaintain the tube non-conductive, a control circuit including a thirdsecondary winding of said transformer to connect said first controlelectrode and cathode across the rails of said stretch, said thirdsecondary winding and the track circuit poled to add their voltages asapplied to the first control electrode to fire the tube when the stretchis unoccupied, and a relay having a winding interposed in said anodecircuit to energize the relay in response to the impulses of currentpassed by said tube.

10. In a track circuit including the rails of a stretch of railway trackand having a source of alternating current connected across the rails atone end of the stretch for energizing track relay means connected acrossthe rails at the other end of the stretch; said track relay meanscomprising, a pairof gas tubes, a pair of electromagnetic relays, astep-up transformer and a power transformer; said power transformerhaving a primary winding powered from said current. source, ananode-cathode circuit for a first one: of said tubes and including afirst secondary winding of said power transformer and a winding: of afirst one of said relays, a control grid-cathode circuit for said firsttube connected across the rails of said stretch and including a secondfiecondary winding of said power transformer,

said track circuit and second secondary winding of the power transformerpoled to add their voltages to fire the tube alternate half cycles ofthe alternating current and energize said first relay when the stretchis unoccupied, said step-up transformer having an input windingconnected across the rails of the stretch to receive energy from saidtrack circuit, said input winding of a preselected impedance topredetermine the maximum rail-to-rail impedance of the track circuit, ananode-cathode circuit for a second one of said tubes and including asecond one of said relays and a secondary winding of said step-uptransformer, a control grid-cathode circuit for said second tubeincluding a third secondary winding of said power transformer to firethe second tube alternate half cycles of the alternating current andenergize said second relay when said step-up transformer is energized bythe track circuit current, said second tube anode-cathode and controlgrid-cathode circuits preselected for the second tube to remainnon-conductive in response to a given variation in the impedance of saidinput winding with respect to said preselected impedance and signalingmeans controlled jointly by said relays.

11. In a track circuit including the track rails of a stretch of track,a source of alternating current having connections to the rails at oneend of said stretch to supply current to the track circuit; an electrontube having an anode, a cathode and at least one control electrode; acontrol electrode-cathode circuit including a current source andconnected across said control electrode and cathode of said tube topredetermine the operating characteristic of the tube, an anode-cathodecircuit for said tube connected across said anode and cathode and havingconnections for receiving current from the rails at the other end ofsaid stretch to effect either a first or a second value of conductioncurrent through the tube solely in response to the current received fromthe track circuit, said conduction current being of said first or saidsecond value according as the stretch is unoccupied and said trackcircuit current flows in the rails at said other end or said stretch isoccupied and the track circuit current is shunted, and a control relaymeans having an element interposed in said anode-cathode circuit andoperated to a first or a second position according as said conductioncurrent is of said first or second value.

12. In a railway track circuit for a stretch of track, a source ofalternating current having connections to the rails of said stretch tosupply alternating current to the track circuit; a first and a secondcontrolled ionization electron tube each having an anode, a cathode andat least one control electrode; an anode-cathode circuit for said firsttube to excite the tube but normally inefiective to fire the tube, acontrol electrode-cathode circuit for said first tube having connectionsto the rails of said stretch to fire the tube on alternate half cyclesof the alternating current when the section is unoccupied, an impedancemeans having connections across the rails of said stretch and of a valuepreselected to pr determine the maximum rai1-to-rai1 impedance of thetrack circuit to govern the response of said first tube to arail-to-rail shunt of the track circuit, an anode-cathode circuit forsaid second tube to excite the tube, a control electrode-cathode circuitfor said second tube having connections for receiving a voltage fromsaid impedance means in response to the track circuit current flowingtherein, said anode-cathode and control electrode-cathode circuits ofthe second tube effective to fire the tube only when the impedance meansis of approximately said preselected value, and signaling meanscontrolled jointly by the anode-cathode circuits of the two tubes.

13. In a railway track circuit for a stretch of track, a source ofalternating current having connections to the rails of said stretch tosupply alternating current to the track circuit; a pair of controlledionization electron tubes each having an anode, a cathode and at leastone control electrode; a first circuit means having connections to theanode and cathode of a first one of said tubes to excite that tube, asecond circuit means receiving power from said track circuit and havingconnections to the control electrode and cathode of said first tube,said first and second circuit means operable to fire the first tube onalternate half cycles of the alternating track circuit current when thestretch is unoccupied and to retain the tube nonconductive when thestretch is occupied by a train to shunt the rails, a transformer havinga primary Winding connected to the rails of said stretch to predetermineby its impedance the maximum rail-torail impedance of the track circuitand govern the shunting sensitivity of the track circuit as provided bysaid first tube, said primary Winding being energized by the alternatingtrack circuit current, means including a voltage source havingconnections to the anode and cathode of a second one of said tubes toexcite that tube, means including a secondary winding of saidtransformer having connections to the control electrode and cathode ofsaid second tube to govern the firing of that tube by said voltagesource according to said energization of said primary winding by thetrack circuit current to check the impedance of the primary winding, andsignaling means governed jointly by the anode-cathode circuits of saidtubes.

JOHN E. HILLIG. EARL W. REICI-I.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,379,592 Miller May 24, 19211,815,960 Young July 28, 1931 1,919,064 Hull July 18, 1933 2,162,859Pelikan June 20, 1939 2,439,680 Volz Apr. 13, 1948

